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Questions tagged [optics]

Optics is the study of light, and its interaction with matter. It includes topics such as imaging systems, fiber optics, lasers, quantum optics, and more.

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Is 1 lux unrealistically low for a cell phone camera flash?

I have a light source which is similar to a typical cell phone camera flash. Based on a measurement and some calculations, I estimated that its illuminance is about 1 lux, or close to twilight values ...
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unusual questions regarding controlling polarized light with LCD shutters

1) Is it correct to assume that if a light is already polarized one of the polarizers on the LCD shutter itself is not required to be present to selectively block it? 2) Is it correct to assume that ...
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1answer
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Reflection Vector (Ray Tracing)

Snell's law of refraction at the interface between 2 isotropic media is given by the equation: \begin{align} \tag{1} n_1 \,\text{sin} \,\theta_1 = n_2 \, \text{sin}\,\theta_2 \end{align} $\qquad$ ...
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What is the relationship between directions in reciprocal and real space of a photonic crystal?

I am reading "Photonic crystals - molding the flow of light" by Joannopoulos et al. (available on-line). The figures below are reproduced from there. This is a diagram of a triangular lattice of air ...
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1answer
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Why does certain clear plastic have an inner glow?

A type of plastic used in packaging for tamper resistant seals appears to have (what I can best describe as) a purplish inner glow under sunlight, and perhaps other bright light. In the image below, ...
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38 views

How does reflective Heads Up Display (HUD) film work?

I've been seeing this reflective HUD film more and more. It seems to let you look through it, but reflects the brighter parts of a display. The end result is similar to a video game where you get a ...
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What is thermo optic effects? [on hold]

I am studying optical mode order converter where it is written that ''Mode control operation by addition of thermo-optic or electrooptic modulation is useful in mode multiplexing–demultiplexing''. ...
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How to capture the electromagnetic waves on camera? [on hold]

can we capture the waves on camera by any means, has it ever done. Is there anything available even theoretical. How to generate the noise in camera.
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1answer
39 views

Laminar Flow From Outdoor Faucet

I ran across a video recently that really caught my attention. It's been circling the internet over the past couple weeks, but I'm trying to figure out what's going on. Basically, it's a video of an ...
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Microscopic bible , how was it made? [on hold]

I once saw a video that during communism or some other era, people used to somehow print whole bibles on a microscopic slide. How could this possibly have been done? Unfortunately i can't find ...
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While flying over Rome we noticed that during sunset, there was a green color between the red and blue of the sunset sky. What causes it?

The picture has only been trimmed and not edited. The green is visible when the red or orange tapers off into the blue. Is this different from what causes the green flash? We were flying from Rome.
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Choice of Unit Cell on Band Diagram (Brillouin Zone Folding)

I am looking at photonic band diagrams specifically, but my question relates to band diagrams in general. For a honeycomb lattice, I can pick a (primitive) rhombic unit cell or a hexagonal unit cell. ...
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Mode matching Gaussian beams [on hold]

I'm coding a Gaussian beam propagation script, and I have the following problem: Given two Gaussian TEM00 beams aligned along the same axis with waist locations $x_1, x_2$; waist $1/e^2$ radii $w_1,...
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1answer
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Why do scratches look radial around a reflected light source?

If you look carefully at your phone screen at a reflected light source - say, a round ceiling light - you might see scratches on your phone around the light being lit up. But curiously they are all ...
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Monochromatic light source through double slits, find the wavelength of the light source? [closed]

The question is "When a monochromatic light source shines through a double slit with a slit separation of 0.20 mm onto a screen 3.5 m away, the first dark band in the pattern appears 9.1 mm from ...
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Addition of 2 planar waves and maximum of real part [on hold]

I'm studying for my optics exam and I'm sitting on this problem which I know is rather basic, but it feels a bit awkward to me. The problem is (roughly translated): for which $\Delta\phi$ is the real ...
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1answer
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Why air spacing for high power beam splitters?

Ordinary glass cube beam splitters are constructed with a dielectric or hybrid coating on the hypotenuse of a right angle prism which is then cemented to another right angle prism. These fail in ...
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1answer
54 views

Can telescope have dual purpose? [duplicate]

Astronomical telescope has a small eye piece and a large objective lens. Whereas a compound microscope has a large eye piece and small objective lens. Therefore can we use astronomical telescope as ...
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1answer
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Distorsion in Photoluminescence

I am studying photoluminescence, but I do not understand why during measurement it turns out that the signal is distorted due to appearance of a long-wavelength replica of the fundamental laser ...
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1answer
30 views

number of photons per area: after reflection != twice the distance

Say we have a light source emitting $N$ photons per unit area. In the first case, the photons are reflected at a distance $r$ from the source and measured again at the source. Divergence caused the ...
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2answers
29 views

Reflectivity with Complex Refractive Index

I would like to ask a followup question on a previous post found here. Starting from the general expression for reflectivity: $$R = \bigl\lvert\frac{n_1-n_2}{n_1+n_2}\bigr\rvert^2$$ and substituting ...
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0answers
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Projection lens [closed]

I need to design a mini projector as a part of a project I am working on. The body of the projector is approximately 7 inch tall and 5 inch wide. I don't know what kind of a lens I need to ensure the ...
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Can light concentrated through convex lens be “cooled down?”

I've just been assigned this biology design project where I'm being tasked to create a device for maximizing "sunlight exposure" of crops and am unsure of this particular question, for the design of ...
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Can traps measure which path in an interferometer?

it is possible in an interferometer to block the paths with screens so that the particle is well located in one of the paths. I wonder if it is the same when instead of screen we use traps in which a ...
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1answer
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Elementary derivation for the minima of the interference pattern in the case of a thin wire without referring to the Babinet principle

For the single slit there is a well known elementary derivation along the following line: If the path difference $\delta$ between the elementary waves coming from the borders of the slit is one wave ...
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1answer
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Non-linear optics - solve differential equations coupled with the finite difference method [closed]

I have these three differential equations in which I need to solve numerically: $$ \frac{dn_0}{dt}= -n_0(t)W_{01}(t) + n_1(t)K_{10} $$ $$ \frac{dn_1}{dt}= -n_1(t)W_{12}(t) - n_1(t)K_{10} + n_2(t)K_{...
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Why are bend losses higher at higher wavelengths in fiber optic cables?

I have been researching the effect of wavelength on macro-bend losses for my extended essay (a 4000 word paper on a subject of your choice, high school level) on fiber optic cables. I asked this ...
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1answer
60 views

Why do cones require more light than rods?

The title says it. In our eyes, why do cones require more light than rods? Like is it because of the energy needed to change the state of the existing atoms, the molecules or what leads to the need of ...
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2answers
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What is the max amount of photons per second of the rods and cones in our eyes?

The title says it all. I just cannot find any information about this - I have tried for so long now. Therefore, I figured that I could reach out to some clever guys in this forum for help instead:) ...
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1answer
37 views

Explain why the following conditions should be satisfied for a sustained interference

My Book says that The following conditions should be satisfied for a sustained interference The two coherent sources placed in front of two slits separated by some distance should be close to ...
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0answers
26 views

Difference between Scattering and Reflection

I am confused: What exactly is the difference between optical scattering and optical reflection? To me, both terms are distinguished by where we place the observation plane. Reflection: Observation ...
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22 views

Feynman’s Treatment of an Opaque Wall

First time poster. I’ve been reading Feynman’s Lectures on Physics, and I’ve just finished reading his treatment on diffraction. Feynman described a method of thinking about an opaque wall that was ...
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Feynman Lecture 33: Fresnel coefficients derivation

The Fresnel coefficients are: $ a=\frac{2\sin\,(r)\cos\,(i)}{\sin\,(i+r)},\quad b=-\frac{\sin\,(i-r)}{\sin\,(i+r)},\quad A=\frac{2\sin\,(r)\cos\,(i)}{\sin\,(i+r)\cos\,(i-r)},\quad B=-\frac{\tan\,(i-r)...
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1answer
27 views

What is a Hollow Core Fiber?

What is the difference between Hollow core Fiber and a normal optical fiber? How does light propagate in a hollow core fiber, what is the mechanism? I want to write a program to simulate the ...
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Difference between free spectral range and chromatic resolution for a Fabry Pérot interferometer

I’m trying to understand intuitively the meaning behind each of these two terms. Here’s my idea of the meanings. The chromatic resolution is the minimum difference in wavelength that can be ...
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63 views

How Diaphragm in Cameras works?

I think I am quite good at math and understand basic geometry, but I have problems understanding the function of a Diaphragm in cameras. Let's say a camera is in a specific state. It captures the ...
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8answers
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Why is angle of incidence equal to angle of reflection?

In the Law of Reflection, the angle of incidence is equal to angle of reflection. Why is this true? This is clearly true experimentally, but how does one prove this true mathematically?
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2answers
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Significance of image position

Consider the case of image formation in the convex lens when the object is placed between f and 2f its image will be formed beyond 2f on the other side. And the image position is said to be the point ...
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1answer
54 views

Measuring the speed of light

Imagine that you have 2 devices in a room (say 2 identical smartphones) and you video-call one another. Once connected, you arrange them in such a way that the outer (not the selfie) camera of the ...
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5answers
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Dependence of lens power on the refractive index of the medium

How does the power of a lens depend on the refractive index of the surrounding medium?
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How does electronic speckle holography produce fringes?

For the out-of-plane set-up shown below, the system is only sensitive to displacements of the object along the z-axis. To create an ESPI image, an image before an after displacing the test object are ...
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Feynman Lecture 33: Are Fresnel coefficients real?

In the Section 33-6 Feynman says: It is possible to go on with arguments of this nature and deduce that $b$ is real. To prove this, one must consider a case where light is coming from both ...
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1answer
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Why is a circular aperture defined by the circle function rather than a heaviside step function?

In the chapter 4 of the text "Introduction To Fourier Optics" by Goodman, the diffraction pattern of light passing through a circular aperture was studied. The diffraction pattern on the image plane $(...
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2answers
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Would the fringe spacing be the same if the slits were at different positions in Youngs double slit experiment?

If the experiment was set up as shown in the image below, where the two slits are at different distances from the screen, would the fringe spacing still be y = ($\lambda)*L/d$ where $\lambda$ is the ...
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1answer
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How are Young's double slit experiment and speckle patterns related?

I know that when light from a laser is reflected from a rough surface onto a screen, it produces a speckle pattern. I believe, a Fourier transform of the intensity distribution of the speckle pattern ...
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2answers
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Slowly-varying envelope approximation: what does it imply?

I understand that the slowly-varying envelope approximation means that we can write an electromagnetic wave as $$ E(x,t)=V(x,t)e^{i(k_0x-\omega_0 t)},$$ where $$ \left \vert \frac{dV}{dx} \right \...
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1answer
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Spin conservation in spontanous parametric down conversion (SPDC)

If ONE pump photon "decays" through the process of spontanous parametric down conversion into TWO photons how can the spin be conserved?
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3answers
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Why do we need a screen to see a real image whereas a virtual image can be seen without a screen?

We did a physics practical in which I couldn't see the image formed by the convex lens without the screen. But I can see the virtual image formed by the plane mirror without a screen.
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Fourier transforming properties of a converging lens

Following Goodman's Introduction to fourier Optics argument I understand that a converging lens will introduce the following difference in optical path (see pag.158, 4th edition) $$r^2/2f$$ where $r$...